The ability to measure an atmospheric concentration of an aerosolized or gaseous compound, such as a volatile organic compound, at relatively low levels, has practical and useful applications, but presents technological challenges.
For example, ethylene is a ubiquitous problem in the fresh produce supply chain. However, measurements of the gas are rarely taken and even more rarely relied upon. Even when used, such measurements often yield highly unreliable results.
While ethylene emitted from produce can be correlated to a degree of ripeness of the produce, almost all ripeness testing is performed using either manual examination by skilled hands, or by destructive cell collapse compression tests wherein cell load capacity is directly proportional to and calibrated to ripeness. Both entail high labour cost, high fruit loss and relatively low accuracy. And, neither test method is informative about the early stages of ripeness, so these methods simply don't work as predictors.
Ethylene control is commonly used across many sectors, but is not typically used for ripeness analysis. And, it is believed that analysis of any VOCs other than ethylene, such as heavier compounds relating to flavor and scent that appear to be present in trace quantities at early phases in the development post-harvest, is unknown, although such other VOCs are believed to provide rich data about fruit condition. Improved measurement capability and sensitivity, such as in a range of 10-30 parts per billion atmospheric, can provide useful tools for early and mid stage fruit analysis.
PPM sensors for, for example, ethylene and a range of other VOCs, are cheap, reliable and simple to use, whereas known sensors suitable in a parts per billion (PPB) range are both expensive and unreliable.
Precision sensors that can test PPB atmospheres cost $10 k and upwards to $1M and take minutes to hours to take single readings, usually by means of long slow flow or super precise measurement tools such as gas chromatography-mass spectrometry (GCMS) and photo acoustic spectrometry. These methods are only suited to very low volume testing.
Hence, a low cost and accurate method and apparatus for measuring low PPB atmospheric concentrations of a substance such as a volatile organic compound is desired.
It is therefore an object of the present invention to provide an apparatus and method for measuring a concentration of a volatile organic compound (VOC) in an atmosphere, and in particular for performing such measurements at low concentration levels.